I used a direct-to-battery outlet for a long time on two different bikes. For charging low-power stuff (like phones), that will be fine for most people.
As soon as I added a second accessory (heated grips, in my case), I installed a
Fuze Block from fuzeblocks.com. There are several similar products, but I picked this one because I could change the fuse in each one of the circuits, and I could simply change any circuit from switched to un-switched. Aside from the battery connections, I tapped in to my license plate light wire to enable the relay. If you plan to install multiple powered accessories, adding some sort of fuse block will avoid a rats' nest of wires connected to your battery.
If you're not familiar with what a relay is, it uses current passing through a low-power wire to close (or "turn on") another circuit. This is the way to provide switched power. I would recommend NOT using power from some existing item (lights, ignition, etc.) because it's too easy to introduce electrical problems. Tapping into an existing wire is one (minor) invasion to the factory wiring, and that's enough for me.
For the record, this was the first time I'd used a Posi-Tap connector (
Posi-Tap- No Crimp Tap) instead of a "cheap" tap connector. They're a bit expensive, but worth it. I'm confident in the tap connection that I use to provide power to the relay.